The present invention relates generally to transluminal application of myogenic cells for tissue repair, such as myocardial repair, and more particularly to balloon catheter protected transluminal application of myogenic cells for repair of a failing body organ such as heart, brain, liver, kidney or pancreas. It is a principal aim of the invention to provide a novel method to repair failing tissue.
In principle, the human body has three types of cells. One type constitutes cells that continuously undergo replication and reproduction, such as dermal cells and epithelial cells of the intestine, for example. These cells, which have a life as short as ten days, are replaced by the same cell type which is replicating continuously. A second type of cell is differentiated in the adult state, but has the potential to undergo replication and the ability to reenter the cell cycle under certain conditions, an example being liver cells. The liver has the capacity to regrow and repair itself even if a tumor is excised and a major portion of the liver is removed. The third cell type comprises those cells that stop dividing after they have reached their adult stage, such as neuro cells and myocardial cells.
For the latter type or group of cells, the number of cells in the body is determined shortly after birth. For example, myocardial cells stop dividing at about day ten after delivery, and for the rest of its life the human body has a fixed number of myocardial cells. Changes in myocardial function occur not by division and new cell growth, but only as a result of hypertrophy of the cells.
Although the absence of cell division in myocardial cells is beneficial to prevent the occurrence of tumorsxe2x80x94which practically never occur in the heartxe2x80x94it is detrimental with regard to local repair capacities. During the individual""s lifetime, myocardial cells are subjected to various causes of damage, that irreversibly lead to cell necrosis or apoptosis.
The primary reason for cell death in the myocardium is ischemic heart diseasexe2x80x94in which the blood supply to the constantly beating heart is compromised through either arteriosclerotic build-up or acute occlusion of a vessel following a thrombus formation, generally characterized as myocardial infarction (MI). The ischemic tolerance of myocardial cells following the shut-off of the blood supply is in a range of three to six hours. After this time the overwhelming majority of cells undergo cell death and are replaced by scar tissue.
Myocardial ischemia or infarction leads to irreversible loss of functional cardiac tissue with possible deterioration of pump function and death of the individual. It remains the leading cause of death in civilized countries. Occlusion of a coronary vessel leads to interruption of the blood supply of the dependent capillary system. After some 3 to 6 hours without nutrition and oxygen, cardiomyocytes die and undergo necrosis. An inflammation of the surrounding tissue occurs with invasion of inflammatory cells and phagocytosis of cell debris. A fibrotic scarring occurs, and the former contribution of this part of the heart to the contractile force is lost. The only way for the cardiac muscle to compensate for this kind of tissue loss is hypertrophy of the remaining cardiomyocytes (accumulation of cellular protein and contractile elements inside the cell), since the ability to replace dead heart tissue by means of hyperplasia (cell division of cardiomyocytes with formation of new cells) is lost shortly after the birth of mammals.
Other means of myocardial cell alteration are the so-called cardiomyopathies, which represent various different influences of damage to myocardial cells. Endocrine, metabolic (alcohol) or infectious (virus myocarditis) agents lead to cell death, with a consequently reduced myocardial function. The group of patients that suffer myocardial damage following cytostatic treatment for cancers such as breast or gastrointestinal or bone marrow cancers is increasing as well, attributable to cell necrosis and apoptosis from the cytostatic agents.
Heretofore, the only means for repair has been to provide an optimal perfusion through the coronary arteries using either interventional cardiologyxe2x80x94such as PTCA (percutaneous transluminal coronary angioplasty), balloon angioplasty or stent implantationxe2x80x94or surgical revascularization with bypass operation. Stunned and hibernating myocardial cells, i.e., cells that survive on a low energy level but are not contributing to the myocardial pumping function, may recover. But for those cells which are already dead, no recovery has been achieved.
The current state of interventional cardiology is one of high standard. Progress in balloon material guide wires, guiding catheters and the interventional cardiologist""s experience as well as the use of concomitant medication such as inhibition of platelet function, has greatly improved the everyday practice of cardiology. Nevertheless, an acute myocardial infarction remains an event that, even with optimal treatment today, leads to a loss of from 25 to 100% of the area at riskxe2x80x94i.e., the myocardium dependent on blood supply via the vessel that is blocked by an acute thrombus formation; A complete re-canalization by interventional means is feasible, but the ischemic tolerance of the myocardium is the limiting factor.
A recent article published in the New England Journal of Medicine (Schxc3x6mig A. et al., xe2x80x9cCoronary stenting plus platelet glycoprotein IIb/IIIa blockade compared with tissue plasminogen activator in acute myocardial infarction,xe2x80x9d N Engl J Med 2000; 343:385-391), for which the applicant herein was the primary clinical investigator, reports on a study of the myocardial salvage following re-canalization in patients with an acute myocardial infarction.
The average time until admission to the hospital in these patients was 2.5 hours and complete re-canalization was feasible after 215 minutes, roughly 3.5 hours. Nevertheless, only 57% of the myocardium at risk could be salvaged by re-canalization through interventional cardiology by means of a balloon and stent. When the group of patients was randomized to the classical thrombolytic therapy, which is the worldwide standard (with no interventional means), only 26% of the myocardium at risk could be salvaged. This means that even under optimal circumstances more than 40% of the myocardial cells are irreversibly lost.
With the knowledge that many patients arrive at a hospital at from 6 to 72 hours after the acute symptoms of vessel blockage by a thrombus, one can assume that the average loss of affected myocardial tissue is in a range of from 75 to 90% following an acute MI.
As noted above, cells can survive on a lower energy level, referred to as hibernating and stunning myocardium. As the collateral blood flow increases or re-canalization provides new blood supply they can recover their contractile function. The principle of myocardial re-perfusion, limitation of infarct size, reduction of left ventricular dysfunction and their effect on survival were described by Braunwald (Braunwald E. et al., xe2x80x9cMyocardial reperfusion, limitation of infarct size, reduction of left ventricular dysfunction, and improved survival: should the paradigm be expanded?,xe2x80x9d Circulation 1989; 79:441-4).
Annually, about five million Americans survive an acute myocardial infarction. Clearly then, loss of affected myocardial tissue is a problem of major clinical importance. Currently, repair is limited to hypertrophy of the remaining myocardium, and optimal medical treatment by a reduction in pre- and after-load as well as the optimal treatment of the ischemic balance by xcex2-blockers, nitrates, calcium antagonist, and ACE inhibitors.
If it were feasible to replace the dead myocardium (scar tissue) by regrowing cells, such a technique would have a profound impact on the quality of life of affected patients.
As noted earlier herein, in addition to ischemic heart disease other reasons exist for the reduction of myocardial cells that contribute to the pumping function of the heart. Among them are the cardiomyopathies, which describe a certain dysfunction of the heart. Reasons are many, such as chronic hypertension which ultimately leads to a loss in effective pumping cells, and chronic toxic noxious such as alcohol abuse or myocarditis primarily following a viral infection. Also, cell damage in conjunction with cytostatic drug treatment is becoming of greater clinical relevance.
The group of Willam C. Claycomb et al. has been engaged in research on the behavior and the development of myocytes since the early 1970""s. In their initial report (Goldstein M. A. et al., xe2x80x9cDNA synthesis and mitosis in well-differentiated mammalian cardiocytes,xe2x80x9d Science 1974; 183:212-3), they described the incorporation of 3H-Thymidin into the nuclei of heart cells of two days old rats which indicates that neonatal cardiac cells still undergo synthesis of DNA and divide despite the presence of contractile proteins. This phenomenon of cell division ceases at day 17 of the postnatal development. After that time no further division of cardiac cells occurs, either in rats or in humans.
The interest in mammalian cardiomyocytes has led to the development of cultures of adult cardiac muscle cells (Claycomb W. C. et al., xe2x80x9cCulture of the terminally differentiated adult cardiac muscle cell: A light and scanning electron microscope study,xe2x80x9d Dev Biol 1980;80:466-482), and ultimately to the generation of a transplantable cardiac tumor-derived transgenic AT1-cell.
During the 1980""s intensive studies were conducted with the characterization of this atrial derived myocyte cell line, which is immortalized by the introduction of the SV40-large-T-oncogene (SV40-T). From this AT-1-cell-group, other adult cardiomyocytes have been derived. These can be passaged indefinitely in culture, can be recovered from a frozen stock, can retain a differentiated cardiomyocyte phenotype, and maintain their contractile activity. They are described as HL-1-cells. The reader is referred, for example, to Delcarpio J. B. et al., xe2x80x9cMorphological characterization of cardiomyocytes isolated from a trans-plantable cardiac tumor derived from transgenic mouse atria (AT-1 cells),xe2x80x9d Circ Res 1991; 69(6):1591-1600; Lanson Jr. N. A. et al., xe2x80x9cGene expression and atrial natriuretic factor processing and secretion in cultured AT-1 cardiac myocytes,xe2x80x9d Circulation 1992; 85(5):1835-1841; Kline R. P. et al., xe2x80x9cSpontaneous activity in transgenic mouse heart: Comparison of primary atria tumor with cultured AT-1 atrial myocytes,xe2x80x9d J Cardiovasc Electrophysiol 1993; 4(6):642-660; Borisov A. B. et al., xe2x80x9cProliferative potential and differentiated characteristics of cultured cardiac muscle cells expressing the SV 40 T oncogene,xe2x80x9d Card Growth Reg 1995; 752:80-91; and Claycomb W. C. et al., xe2x80x9cHL-1 cells: A cardiac muscle cell line that contracts and retains phenotypic characteristics of the adult cardiomyocyte,xe2x80x9d Proc Natl Acad Sci USA 1998; 95:2979-84.
Finally, the cardiomyocyte transplantation in a porcine myocardial infarction model has been studied intensively in collaboration with the research group of Frank Smart (Watanabe E. et al., xe2x80x9cCardiomyocyte transplantation in a porcine myocardial infarction model,xe2x80x9d Cell Transplant 1998; 7(3):239-246). In conjunction with the AT-1 cardiomyocytes, human fetal cardiomyocytes were injected into the adult pig heart infarction area.
In summary, these cells showed local growth and survived in the infarction border zone, but could not be found in the core scar tissue of the myocardial infarction. The majority of the implanted cells were replaced with inflammatory cells, suggesting that the immuno-suppressant regimen that was concomitantly applied was not sufficient for the grafted cells to survive in the host myocardium. Other factors that may have influenced the result that the transplanted cells were not detected, could possibly be linked to the fact that the cells were grafted 45 days after inducing the infarction.
It is known that the inflammatory stimuli for cell growth are significantly reduced in the first two to three weeks of an MI. Also, that transforming-growth-factor-b (TGF-b), fibroblast-growth-factor-2 (FGF-2), platelet-derived-growth-factor (PDGF) and other cytokines, like the interleucin-family, tumor-necrosis-factor-a (TNF-a) and interferon-g are strong stimulators of cell proliferation and cell growth. The adjunct therapy with immuno-suppression has further reduced this stimuli for cell growth.
Another major factor for the failure of detection of grafted cells in the myocardial scar may be the selection of the infarction model. An artery is occluded and the blood supply has not recovered before grafting. There is no reason to assume that the grafted cells could survive in an ischemic area and grow, better than the myocytes.
Therefore, other groups have tried to induce a myocardial angiogenesis by gene-therapy. This was either performed by the administration by fibroblast growth factor II in the presence or absence of heparin (see Watanabe E. et al., xe2x80x9cEffect of basic fibroblast growth factor on angiogenesis in the infarcted porcine heart,xe2x80x9d Basic Res Cardiol 1998; 93:30-7) or by application of vascular endothelial growth factor (VEGF), a potent mitogen for endothelial cells. VEGF stimulates capillary formation and increases vascular permeability (Lee J. S. et al., xe2x80x9cGene therapy for therapeutic myocardial angiogenesis: A promising synthesis of two emerging technologies,xe2x80x9d Nat Med 1998; 4(6):739-42). Still other groups have tried to increase the collateral capillary blood flow by human bone marrow derived angioblasts and have shown an improvement in acute myocardial infarction in rats treated with injections of colony-stimulating-factor-G (CSF-G) mobilized adult human CD-34 cells (Kocher A. A. et al., xe2x80x9cNeovascularization of ischemic myocardium by human bone-marrow-derived angioblasts prevents cardiomyocyte apoptosis, reduces re-modeling and improves cardiac function,xe2x80x9d Nat Med 2001; 7(4):430-6).
While these approaches certainly have some research merit, their clinical relevance for the majority of patients is not as important, since we have effective means to re-canalize an occluded vessel and provide a blood supply via the natural branching of the coronary arteries, which further subdivides into arterioles and capillaries.
Other attempts to transplant preformed patches also necessitate the growth of the grafted cells in a patch formation and a surgical operation in a patient, which requires opening the thoracic cage.
Considering the complications, the cost and the risk associated with these time consuming procedures, it becomes clear that they offer only limited likelihood for widespread routine application.
Other groups have tried to make use of the precursor cells that are found in the peripheral muscle. Unlike the heart, there is a certain degree of repair in peripheral skeletal muscles, since the peripheral skeletal muscle contains progenitor cells, which have the capability to divide and replace the peripheral muscle. By isolating those cells from a probe of a thigh muscle, the progenitor cells of skeletal muscle have been separated, cultured and re-injected in an animal model (Taylor D. A. et al., xe2x80x9cRegenerating functional myocardium: Improved performance after skeletal myoblast transplantation,xe2x80x9d Nat Med 1998; 4(8):929-33; Scorsin M. et al., xe2x80x9cComparison of the effects of fetal cardiomyocyte and skeletal myoblast transplantation on postinfarction left ventricular function,xe2x80x9d J Thorac Cardiovasc Surg 2000; 119:1169-75), and more recently in some patients also.
The application of these cultured cells also been attempted by injection with small needles following an opening of the subject""s chest and the pericardial sac. While in the model of kiyo-infarction, in which only the myocardial cells die but the blood supply through the vascular system is not limited, the injection of autologous skeletal myoblasts improves the myocardial function. The results indicated, however, that the engrafted cells retain skeletal muscle characteristic, which means they cannot contract at the constant fast rate imposed by the surrounding cardiac tissue. In addition, no electrical connection exists between the graft cells and the host tissue, and it is assumed that their contribution to improve contractile performance probably resulted from the mechanical ability of the engrafted contractile tissue to respond to stretch activation by contraction.
Considering the experience with latissimus dorsi muscle graftingxe2x80x94a procedure called dynamic cardiomyoblastyxe2x80x94, the disappointing results with the possible use of skeletal muscle as a myocardial substitute indicate that the long term different muscle characteristics of skeletal muscles do not match the need of a constantly pumping myocardial cell. Therefore, the best these cells might achieve would be to improve the quality of the scar of the ischemic myocardium, but not actively contribute to a contraction of this area in the long term.
The present invention is directed to interventional cardiology through an intraluminal application of cells that have the capability to replace the necrotic tissue of a failing organ, such as myocardial tissue in the case MI of the heart, to resume the myocardial function and therefore improve the pumping performance of the myocardium. The procedure is oriented on the clinical practice of interventional cardiology following the principle that only those approaches that are both (a) relatively easy to perform, with little or no risk to the patient but a potentially high benefit, and (b) highly cost effective, are likely to be routinely applied in everyday medicine.
An important aspect of the invention is that the cells to be used in the intraluminal or transluminal application preferably are autologous adult stem cells, which are derived from the same patient that has suffered the infarction. The cells are harvested and separated before injection, from the same individual (autologous transplantation). In a case of failing tissue of the myocardium, these cells are then injected into the coronary artery that caused the infarction.
The approach taken according to the invention recognizes that the stem cells need a certain contact time to adhere and migrate from the vascular bed into the infarcted myocardial area. In contrast to previous approaches, in which patches or applications through needles into the infarcted area have been considered, the approach of the invention hypothesizes that the most effective way to deliver the cells to the infarcted area is through the vascular tree of coronary arteries, arterioles and capillaries that supply the infarcted area. An occlusion balloon of an over the wire type catheter is inflated at the site of the primary infarction, after the vessel has been re-canalized and the blood flow reconstituted.
Importantly, while the blood flow is still blocked, the stem cells are supplied by slow application through the balloon catheter over a relatively short period of time, on the order of 15 minutes, for example. That is, the stem cells are injected through the inner lumen of the catheter while the balloon is inflated, and therefore, no washout occurs. It is believed by applicant that this intracoronary or transcoronary application of cells during a period that perfusion is ceased is critical to enabling the cells to successfully attach to the vessel or myocardial wall. And further, to overcome more actively the endothelial barrier following the increased pressure in the vascular bed, which is attributable to the fact that the retrograde blood flow is limited through the inflated balloon catheter.
The principles of the invention are not limited to cellular repair of damaged or failing myocardial tissue, but may be applied in processes for repair of tissue of various organs of the body, including the brain, liver, kidney or pancreas, for example.